Inexorable advances in consumer electronics have led to affordable digital video devices capable of rendering crisp images with high fidelity audio. The emergence of digital video devices with recording capability represents a significant threat to content providers, since the content of high quality digital programs can be easily duplicated. The motion picture, film and video industry estimate that substantial sums have been lost annually due to unauthorized duplication. Such unauthorized duplication deprives the rightful owners or distributors of program content of their income and reduces their incentive to produce new movies and videos. Thus, the protection of program contents especially high definition digital program content, from unauthorized copying is an important problem facing the consumer electronics industry.
Due to the need for a secure transmission of programs, a number of video encoding or scrambling techniques have been developed to provide control over potential recipients and to prevent unauthorized use of received transmissions. For instance, to block reception by non-subscribers, television subscription networks typically encode or scramble the distributed television signals, thereby defeating acceptable display of those television signals by non-subscribers who do not have the proper decoders or descramblers.
However, an authorized subscriber may simply connect a video recorder to his decoder to record for subsequent and repeated viewing a desired program that is distributed over the subscription network. Such recording for later viewing decreases the market interest in subsequent distribution of that program over the subscription network. For instance, xe2x80x9cpay per viewxe2x80x9d broadcasts contemplate a once-only distribution of video programming such as first run motion pictures, popular sporting events and special entertainment events to subscribers who are charged a one-time fee to receive that particular program. Such one-time broadcasting is quite sensitive to unauthorized reproductions which erode the value of the content of the pay-per-view transmission.
Since the scrambling or encoding of the video signal cannot prevent a paying subscriber from recording the program, it is desired that the video signal be modified so that the subscriber can view the program, but the operation of recording equipment should.be defeated or tightly controlled to avoid unauthorized recording.
Traditionally, with monitors or display devices that accept analog input signals, methods for making the video signal non-recordable have relied upon adjusting an automatic gain control (AGC) circuit normally included in a videotape recorder. Other techniques for modifying the video signal to prevent its recording or reproduction rely on the relative sensitivity of a vertical sync detection circuit normally provided in videotape recorders. The removal of a portion of the pulses intended for a vertical blanking interval causes a vertical synchronizing detector included in most videotape recorders to be unable to detect those vertical sync pulses, resulting in a loss of control information needed for the proper operation of the videotape recorder.
The advent of digital video recorders that accept high definition analog video inputs has necessitated new solutions for protecting the high definition content. Methods have been developed for encrypting digital data for transmission over high speed digital interfaces, such as IEEE-1394. However, there presently is not a cost-effective digital transmission interface for transmitting uncompressed high definition digital video for consumer applications which require transmission rates of greater than 1 Gigabit/second. For example, the fastest current IEEE-1394 interface standard supports transmission rates of less than 400 Megabits/second. Using compressed bitstreams to transfer the digital data from the set top box to the receiver is problematic because the transmitter needs a high definition Motion Pictures Experts Group (MPEG) encoder to handle locally generated video information such as on screen displays or electronic program guides. Additionally, high definition MPEG encoders are not cost effective for consumer applications.
The invention provides a transmitter for encoding video transmission to a receiver, the transmitter and the receiver communicating over a digital interface and a video interface. The digital interface communicates a frame key encrypted between the transmitter and the receiver, while the video interface having a color component signal. The transmitter includes a sequence generator adapted to receive the original frame key and to generate a sequence of pseudo-random values for the color component; and a transformation circuit connected to the sequence generator and to the color component signal for providing an encoded color component signal.
Implementations of the invention include one or more of the following. A range clamp may be positioned between the color component signal and the transformation circuit for restricting the value of the color component signal to a predetermined range. An encrypted region generator may be connected to the transformation circuit for limiting the set of transformed pixels to a predetermined region of a video frame. The transformation circuit may be an adder. A new offset may be generated for each scan line. A delay memory for time-shifting the output of the transformation circuit may be used.
In a second aspect, a receiver decodes video transmission from the transmitter. The receiver includes a decryptor sequence generator adapted to receive and decrypt the frame key and to generate a sequence of pseudo-random values for the color component; and an inverse transformation circuit connected to the decryptor sequence generator and to the color component signal for decoding the color component signal.
Implementations of the invention include one or more of the following. The inverse transformation circuit includes a subtractor for subtracting the pseudo-random value from the color component signal. A comparator may be connected to the subtractor, the comparator determining whether the output of the subtractor exceeds a minimum value; a multiplexer may be connected to the comparator and receiving a first value and a second value, the multiplexer outputting the first value if the output of the subtractor exceeds the minimum value and otherwise outputting the second value; and an adder may be connected to the multiplexer and to the subtractor. A gain/offset adjuster may be connected to the adder. The transmitter may have a delay memory for time-shifting of pixel values to be transmitted. A receiver delay memory may be used for inverse time-shifting of transmitted pixel values. A pixel clock generator may be connected to the color component signal for generating a clock signal. The pixel clock generator includes a phase locked loop which aligns the clock signal with a video sync pulse.
In another aspect, a method for controlling reproduction of video transmission between the transmitter and the receiver, including: communicating a frame key over the digital interface; generating a sequence of pseudo-random offsets for the color component signal based on the unencrypted frame key; generating an encoded color component signal using one of the pseudo-random offsets; and transmitting the encoded color component signal over the video interface.
Implementations of the invention include one or more of the following. The method includes seeding a pseudo random number generator with the encrypted frame key. The method includes periodically generating a new encrypted frame key; and initializing a pseudo random number generator with the new encrypted frame key. The method includes scaling the color component signal with a predetermined ratio; and adding an offset to the scaled color component signal. The method includes clamping the color component signal within a predetermined range. The clamping step further determining if the value of the color component signal is less than a first value and if so, setting the value of the color component signal to the first value; and determining if the value of the color component signal is greater than a second value and if so, setting the value of the color component signal to the second value. The method includes determining whether each pixel is in an encrypted boundary; and transmitting the pixel unencrypted if the pixel is outside of the encrypted boundary. The method includes converting the encoded color component signal to an analog signal. The method includes shifting each pixel value in time within the predetermined pixel range, wherein the shifting further comprises providing the encoded color component signal to a delay memory. The method includes decrypting the color component signal sent over the video interface by receiving the encrypted frame key over the digital interface; generating a sequence of pseudo-random offsets for the color component signal based on the encrypted frame key. A pseudo random number generator may be generated with the frame key. The method may subtract the pseudo-random offset from the encoded color component signal. The method includes compensating for out-of-range values associated with the subtracting step and/or resealing the color component signal to its original input range. The method includes shifting each pixel value within the predetermined pixel range prior to the step of transmitting the encoded color component signal over the video interface. The method includes undoing the pixel shift operation using a delay memory. The method includes displaying the color component signal after decrypting the encoded color component signal.
In another aspect, a method for controlling the reproduction of a video transmission between the transmitter and the receiver includes authenticating the transmitter and the receiver using the digital interface; periodically transmitting an encrypted frame key to the receiver over the digital interface; generating a pseudo-random offset at the transmitter for each color component signal during an active part of a scan line; applying the pseudo-random offset to the color component signal to generate an encoded color component signal; transmitting the encoded color component signal over the video interface; generating the pseudo-random offset at the receiver based on the decrypted frame key; removing the pseudo-random offset from the encoded color component signal transmitted over the video interface to generate a decoded color component signal; and displaying the decoded color component signal on a display device.
In another aspect, a system controls the reproduction of video transmission between the transmitter and the receiver. The system having an encryptor with an offset generator adapted to receive the original frame key and to generate a sequence of pseudo-random values for the color component; and an adder connected to the offset generator and to the color component signal for providing an encoded color component signal. The system also having a decryptor with a decryptor offset generator adapted to receive and decrypted the frame key and to generate a decryptor pseudo-random value for the color component; and a subtractor connected to the offset generator and to the color component signal for subtracting the offset signal from the color component signal.
Implementations of the invention include one or more of the following. The color component signal includes one of red, green and blue (RGB) video signals, one of luminance and chrominance video signals, or a black and white video signal.
Advantages of the invention include one or more of the following. The invention controls the recording and reproduction of high quality program content, particularly when the program content is transmitted from one consumer device, such as a set-top box or a personal computer, to another consumer device, such as a monitor. Unauthorized duplication or piracy of high quality program content from digital storage media, cable and broadcast television material is avoided. The security of the video transmission is achieved while maintaining a high picture quality. By operating on the video output signals, the invention avoids the need to compress the entire high definition program locally with information generated by on screen display devices (OSDs) or other graphic devices such as 3D video controllers. The invention also avoids the need to decompress the video bitstream at the receiver. The piracy protection of the program content is achieved cost effectively.